Water-based fluorescent ink, recorded image using the same, and judging method

ABSTRACT

The present invention relates to a water-based fluorescent ink for the purpose of measurement or judgment of the fluorescence emission in a visible light region by an excitation wavelength in a predetermined ultraviolet range, containing water, a coloring material dissolved or dispersed in water, and an organic solvent, having a plurality of fluorescent groups in the coloring material structure of the coloring material, and using a water-soluble coloring material having a sulfonic acid group as the water-soluble group in the state of a free acid, capable of improving the water resistance and the light resistance, dramatically increasing the content of the fluorescent coloring material in the ink, which has conventionally been included only by a small amount in the ink due to the concentration quenching problem, obtaining preferable fluorescence emission and water resistance of the recorded image, and providing preferable adhesion resistance to the recording medium of the coloring material and reliability.

This application is a continuation of International Application No.PCT/JP03/08102, filed on Jun. 26, 2003, which claims the benefit ofJapanese Patent Application No. 2003-127617, filed on May 2, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-based fluorescent ink forproviding fluorescence emission for the purpose of measurement orjudgment in a visible light region. More specifically, the presentinvention relates to a water-based fluorescent ink that enables visualrecognition of a recorded image under UV light irradiation but not underordinary visible light, a water-based fluorescent ink that fluorescesunder UV light but not under ordinary visible light, and an authenticityjudging method using the above-mentioned ink.

2. Related Background Art

Recently, various characteristics are required water-based ink forfurther various applications, in addition to the conventional coloringpurpose for recording an image such as characters, graphics, or the likeon a recording material. In particular, use of an ink containing afluorescence emitting component is applied not only for improving thevisual color saturation of an obtained image, but also for amusement,and the purpose of the identification and classification, security, orthe like. Water-based inks for various applications are now required.Such applications include, not only the formation of a beautiful colorimage, but also development of the technique for recording informationsuch as characters, numbers, marks, and bar codes on a recording mediumwith a fluorescent ink that emits colored fluorescence under irradiationof ultraviolet light of an appropriate wavelength to provideinformation, e.g., security information, other than ordinary visualinformation. In particular, in a system for authenticity judgment(forgery prevention) or security information, a device reads intensityof fluorescence emitted from a fluorescent coloring material underirradiation of light of a reference wavelength (reference excitationwavelength, for example, 254 nm) for judgment or measurement.

Heretofore, various water-based fluorescent inks for the above-mentionedapplication have been proposed, discussed and reported to improve thewater resistance and color properties including the fluorescence of therecorded image. Since a water-based ink can contain a water-solublefluorescent material only in a small amount because of the concentrationquenching phenomenon (a phenomenon that the fluorescence decreases asthe content of the coloring material in the ink increase), it isdifficult to enhance the fluorescence intensity. Moreover, conventionalfluorescent inks contain a coloring material having a good dissolvingproperty to prevent aggregation and association to obtain strongerfluorescent intensity, resulting in poor water resistance of the image.

On the other hand, when a compound that forms a salt with an aqueousfluorescent coloring material, e.g., a cationic compound that forms asalt with an acidic dye, is used to improve the water resistance, thewater resistance is improved but the fluorescent property isdeteriorated drastically.

To cope with this problem, Japanese Patent Application Publication No.H8-053640, for instance, proposes a water-based fluorescent inkcontaining an aqueous fluorescent dye in an emulsion or in capsuledform, whereby the water resistance is improved dramatically incomparison with conventional water-based fluorescent inks, and, evenwhen the content of the emulsion or capsules containing the aqueousfluorescent dye in the ink is increased, aggregation or association ofthe aqueous fluorescent dye would not occur, and thus the fluorescentproperty can hardly be deteriorated. However, when the water or solventcontent in the ink decreases, the ink is subject to thickening leadingto insufficient sticking resistance. Moreover, when it is used for theink jet recording method, the sticking resistance in the nozzle isinsufficient. In the worst case, the nozzle is blocked with the ink.Furthermore, with the thermal ink jet recording method, koga deposits onthe heater surface so that the ejection reliability is deteriorateddrastically.

SUMMARY OF THE INVENTION

The present invention is to solve the above-mentioned problems ofconcentration quenching and water resistance. More specifically, theobject of the present invention is to provide a water-based ink that canimprove both fluorescence properties and water resistance of the image,which has been difficult with conventional fluorescent coloringmaterials, and can contain a large amount of a fluorescent coloringmaterial, and in addition, can have improved sticking resistance andreliability. The present invention also provides a recorded image and ajudging method using the above-mentioned ink.

The above-mentioned object can be achieved by the following embodiments.

1. One aspect of the present invention is a water-based fluorescent inkto be used for measurement or judgment of a fluorescence in a visiblelight region that is emitted by irradiation of an excitation light of apredetermined excitation wavelength in an ultraviolet region, which inkcomprises water, a coloring material that dissolves or disperses inwater, and an organic solvent, wherein the coloring material has aplurality of fluorescent groups and a sulfonic acid group as awater-soluble group in a structure thereof in the state of a free acid.

2. Another aspect of the present invention is a water-based fluorescentink to be used for measurement or judgment of a fluorescence in avisible light region emitted by irradiation of an excitation light of apredetermined excitation wavelength in an ultraviolet region, which inkcomprises water, a coloring material that dissolves or disperses inwater, and an organic solvent, wherein the coloring material has aplurality of fluorescent groups and a sulfonic acid group as awater-soluble group in a structure thereof in the state of a free acid,and wherein the ink is visible under an ordinary light in a visiblelight region.

3. Still another aspect of the present invention is a recorded imageformed with a water-based fluorescent ink to be used for measurement orjudgment of a fluorescence in a visible light region that is emitted byirradiation of an excitation light of a predetermined excitationwavelength in an ultraviolet region, wherein the ink comprises water, acoloring material that dissolves or disperses in water, and an organicsolvent, and wherein the coloring material has a plurality offluorescent groups and a sulfonic acid group as a water-soluble group ina structure thereof in the state of a free acid.

4. Still another aspect of the present invention is a method for judgingauthenticity of an ink which comprises a step of irradiating anultraviolet ray to an image formed with a water-based fluorescent ink,wherein the water-based fluorescent ink emits a fluorescence in avisible light region by irradiation of an excitation light of apredetermined excitation wavelength in an ultraviolet region, andwherein the ink comprises water, a coloring material that dissolves ordisperses in water, and an organic solvent, wherein the coloringmaterial has a plurality of fluorescent groups and a sulfonic acid groupas a water-soluble group in a structure thereof in the state of a freeacid.

5. Still another aspect of the present invention is a method for judgingauthenticity of an image which comprises a step of irradiating anultraviolet ray to an image formed with a water-based fluorescent ink,wherein the water-based fluorescent ink emits a fluorescence in avisible light region by irradiation of an excitation light of apredetermined excitation wavelength in an ultraviolet region, andwherein the ink comprises water, a coloring material that dissolves ordisperses in water, and an organic solvent, wherein the coloringmaterial has a plurality of fluorescent groups and a sulfonic acid groupas a water-soluble group in a structure thereof in the state of a freeacid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the fluorescence intensity when inks ofExamples 1 to 3 left at 60° C. are excited at an excitation wavelengthof 254 nm.

FIG. 2 is a graph showing the fluorescence intensity when inks ofComparative Examples 1 to 3 left at 60° C. are excited at an excitationwavelength of 254 nm.

FIG. 3 is a graph showing the fluorescence intensity when printed imageswith inks of Example 4 and Comparative Examples 4 and 5 are excited atan excitation wavelength of 254 nm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, with reference to the preferable embodiments of the invention, thepresent invention will be explained in further details. First, thepredicted mechanism of the inks of the present invention will beexplained.

In general, the conventional water-based fluorescent ink using a monomerwater-soluble fluorescent dye cannot contain the dye in a large amountbecause of the so-called concentration quenching, a phenomenon that thefluorescent intensity decreases as the dye concentration in the inkincreases due to the dye association or aggregation. Also, conventionalink uses a highly soluble dye to obtain good fluorescent properties, sothat the water resistance of the conventional ink is not satisfactory.

In contrast, the ink of the present invention solves these problems byusing a coloring material having a plurality of fluorescent groups and asulfonic acid group as the water-soluble group.

That is, since the coloring material used in the present invention has aplurality of fluorescence-emitting groups (fluorescent luminophores) inthe structure, and a sulfonic acid group as the water-soluble group, thecoloring material is hardly in an associated state in the ink.Furthermore, the ink can contain the coloring material in a largeramount and a plurality of the fluorescent groups do not cause theassociation state that decrease fluorescence. That is, since theassociation with regularity is hard to occur and at least part of thefluorescent groups function, the fluorescent property is hardlyaffected.

In particular, when the fluorescent group has a water-soluble group,particularly a sulfonic group, the water molecules gather around thefluorescent groups resulting in good fluorescence, and thus it ispreferable. Moreover, since water molecules gather around the sulfonicgroups, the sticking resistance of the ink is improved.

Furthermore, when the above-mentioned ink is applied onto a recordingmaterial for recording to dye the components of the recording material,the fluorescence emission is hardly be lowered so that a preferablefluorescent image can be obtained from the same reason as mentionedabove.

Moreover, when the coloring material included in the ink of the presentinvention is hardly water-soluble, the image formed on the recordingmaterial can have good water resistance. Furthermore, when an organicsolvent that can dissolve the coloring material more than water does isused for the ink of the present invention, fluorescence is enhancedbecause when the ink is applied to a recording material such as acommercial bond paper, the surface of the cellulose fiber is wetted withthe organic solvent containing the colorant to achieve good dyeingconditions, i.e., dyeing in a monomolecular state. In this case, whenthe solubility of the coloring material in water is less than 3% by massat an ordinary temperature, the effect of the present invention becomesmore conspicuous. Furthermore, when the solubility of the coloringmaterial used in the present invention in the organic solvent is 3 wt %,higher than in water, better results can be obtained.

Moreover, when the coloring material used in the ink of the presentinvention has direct property, the preferable effects can be obtained interms of the fluorescent emitting property and water resistance. It ispreferable for the coloring material used for the ink of the presentinvention to have substantivity, because it can form hydrogen bondingmore easily with the constituent of the recording material, that is, itcan bind to the cellulose in a mostly monomolecular state when appliedonto a commercially available bond paper. As a result, the fluorescenceis improved. Further, as the coloring material becomes more insoluble inwater owing to binding reaction between the coloring material andcellulose such as hydrogen bonding. the preferable water resistance canbe obtained.

Moreover, it is preferable that a plurality of the fluorescent groupspresent in the structure of the coloring material used for the ink ofthe present invention are linked by a linking group.

When a plurality of the fluorescent groups linked by a linking group arepresent in the coloring material structure, the fluorescence hardlydecreases. A linking group not having resonance, such as a triazinering, is particularly preferable.

The fluorescent group means a group that fluoresces in the visible lightregion by excitation with light such as ultraviolet light.

The water-soluble coloring material used in the ink of the presentinvention, having a plurality of the fluorescent groups and a freesulfonic group as a water-soluble group, fluoresces when irradiated withlight of a predetermined excitation wavelength, and the wavelength ofthe fluorescence differs from that of the excitation light. Theexcitation wavelength and the fluorescence wavelength include theultraviolet region, the visible light region, the infrared light range,and the near infrared light range.

Specific examples of the basic structure of fluorescent group andlinking group are shown below, but not limited thereto. The fluorescentgroup and linking group included in a molecule are not limited to theone kind, and as long as the effect of the present invention issatisfied, any groups can be selected and combined. Moreover, awater-soluble group, such as a hydroxyl group and a sulfonic acid group,may be present in the basic structure of the fluorescent group, as longas the fluorescent property is not influenced significantly.

The presence of the linking group can provide the coloring material witha three-dimensional structure to prevent the association between thecoloring material molecules, thereby preventing decrease in fluorescenceintensity owing to the concentration quenching.Basic Structure

Atomic Group Including the Linking Group

(Z in the above-mentioned formulae (1) to (3) each independentlyrepresents an NR₁R₂, an SR₃ or an OR₃, Y in the formula (2) representsan H, a Cl, the above-mentioned Z, an SR₄ or an OR₄, E in the formula(3) represents a Cl or a CN. R₁, R₂, R₃ and R₄ each independentlyrepresent an H, an alkyl group, a substituted alkyl group, an arylgroup, a substituted aryl group, an aralkyl group, a substituted aralkylgroup, or a hydroxyl group. R₁ and R₂ may form a 5- or 6-membered ringtogether with a nitrogen atom.

(In the above-mentioned formula (4), R₅ is selected independently from ahydrogen atom, an alkyl group, a substituted alkyl group, an alkoxygroup, a halogen atom, a CN, a ureid group, and an NHCOR₆. The R₆ isselected from a hydrogen atom, an alkyl group, a substituted alkylgroup, an aryl group, a substituted aryl group, an aralkyl group and asubstituted aralkyl group. In the formula (5), T represents an alkylgroup, and W is selected from a hydrogen atom, a CN, a CONR₇R₈, apyridium group, and a carboxyl group. R₇ and R₈ each independentlyselected from a hydrogen atom, an alkyl and a substituted alkyl group. Mrepresents an alkylene chain having 2 to 8 carbon atoms. In the formula(6), B is selected from a hydrogen atom, an alkyl group and a carboxylgroup.

The specific examples of the substituents in the above general formulascan be selected according to the desired fluorescence emitting property.

Examples of the water-soluble fluorescent coloring material having aplurality of fluorescent groups and a free sulfonic acid group as thewater-soluble group in the coloring material structure to be used in thepresent invention, which have the above-mentioned atomic groups as thebasic structure and linking group, are shown below but not limitedthereto.

Moreover, the particularly preferable water-soluble fluorescent coloringmaterials having a plurality of fluorescent groups and at least one freesulfonic acid group as the water-soluble group are those having astilbene group as the fluorescent groups. Particularly preferable onesare those having a plurality of diamino stilbene disulfonic acidstructures. One preferable example of such coloring materials, which hasan absorption spectrum in the visible light region and is visible, isCompound (A) shown below, but not limited thereto.

The fluorescent ink of the present invention may further contain anon-fluorescent water-soluble coloring material. In conventionalfluorescent ink, the presence of such a non-fluorescent water-solublecoloring material decreases the fluorescence to a great extent, and insome cases the fluorescence is quenched. The ink of the presentinvention can prevent such deterioration of the fluorescence emission.

The water-soluble coloring material means those having a water-solublegroup such as a sulfonic acid group, a carboxylic acid group, aphosphoric acid group, a hydroxyl group, and an amino group in a freestate in the structure, and capable of existing stably in water withoutthe aid of a second component such as a surfactant and a resin. Thespecific examples thereof are, for example, direct dyes, acidic dyes,basic dyes, vat dyes and the like. Specifically, for example, Directblack 168, direct Black 154, Direct Yellow 142, Direct Yellow 86, directRed 227, Direct Blue 199, Direct Yellow 142, Direct Black 195, and FoodBlack 1,2 can be presented, but not limited thereto. The water-solublecoloring materials can be used alone, or as needed, in combination oftwo or more kinds.

Moreover, depending on the cases, among the above-mentionedwater-soluble coloring materials, those having a low water solubilityand a pigment-like behavior may be used as the water-dispersiblecoloring materials. When such a coloring material is used together inthe ink of the invention, the decrease in fluorescence emission isgreatly alleviated.

Specific examples of the non-fluorescent coloring material having acarboxylic group as the water-soluble group include di or tris azocoloring materials of strong substantivity such as Direct black 195,Direct Black 51, or the like, and coloring materials having a dimmerstructure or the linking group the following coloring materialsrepresented by the general formulae (A) to (C) in a free acid state.According to the present invention, even when the above-mentionedcoloring material coexists in the ink, the decrease in fluorescenceemission can be greatly alleviated. Those capable of providing theeffects of the present invention when used in combination are notlimited to the above-mentioned coloring materials.

(1) Coloring Materials Represented by the Following General Formula (A)in the Form of Free Acid:

General Formula (A)Pc(SO₃H)_(t) (SO₂-NR¹-L-NR²-X-NR³-G)_(q)

[In the general formula (A), Pc represents a metal containingphthalocyanine nucleus, and R₁, R₂ and R₃ each independently representan H, an alkyl group, a substituted alkyl group, an alkenyl group, asubstituted alkenyl group, an aralkyl group or a substituted aralkylgroup. L represents a divalent organic linking group. X eachindependently represents a carbonyl group or a group represented by thefollowing formulae (2) to (4).

(Z in the above-mentioned formulae (2) to (4) each independentlyrepresents an NR₄R₅, an SR₆ or an OR₆, Y in the formula (3) representsan H, a Cl, the above-mentioned Z, an SR₇ or an OR₇, E in the formula(4) represents a Cl or a CN. R₄, R₅, R₆ and R₇ each independentlyrepresent an H, an alkyl group, a substituted alkyl group, an arylgroup, a substituted aryl group, an aralkyl group, or a substitutedaralkyl group. R₄ and R₅ form a 5- or 6-membered ring together with anitrogen atom.) G represents a colorless organic residual groupsubstituted by one or two COSH or COOH, and t+q is 3 or 4.]

As the compounds represented by the general formula (A), for example,those mentioned below can be presented.

(2) Coloring Materials Represented by the Following General Formula (B)in the Form of Free Acid:General formula (B)Ar¹N═NJX(NR¹LNR²X)_(n)JN═NAr²

[In the above-mentioned general formula (B), J represents the followingformula.

In the general formula (B), Ar¹ and Ar² each independently represent anaryl group or a substituted aryl group, and at least one of Ar¹ and Ar²each independently has at least one substituent selected from COOH andCOSH. R₁ and R₂ each independently represent an H, an alkyl group, asubstituted alkyl group, an alkenyl group, or a substituted alkenylgroup. L represents a divalent organic linking group, and n represents 0or 1. X each independently represents a carbonyl group or a grouprepresented by the following formulae (2) to (4).

(Z in the above-mentioned formulae (2) to (4) each independentlyrepresents an NR₃R₄, an SR₅ or an OR₅, Y in the formula (3) eachindependently represents an H, a Cl, the above-mentioned Z, an SR₆ or anOR₆, E in the formula (4) represents a Cl or a CN. R₃, R₄, R₅, and R₆each independently represent an H, an alkyl group, a substituted alkylgroup, an alkenyl group, a substituted alkenyl group, an aryl group, asubstituted aryl group, an aralkyl group, or a substituted aralkylgroup. R₃ and R₄ form a 5- or 6-membered ring together with a nitrogenatom.) The compound represented by the general formula (B) has at leastthe same number of a group selected from COOH and COSH as that of SO₃Hgroup.]

As the compounds represented by the general formula (B), for example,those mentioned below can be presented.

(3) Coloring Materials Represented by the Following General Formula (C)in the Form of the Free Acid:

[In the above-mentioned general formula (C), Ar and Ar¹ eachindependently represent an aryl group or a substituted aryl group, andat least one of Ar and Ar¹ has a substituent selected from the groupconsisting of a sulfonic group, a carboxyl group and a thiocarboxylicgroup. J and J1 are each independently represented by the followingformulae (2), (3) or (4).

(In the above-mentioned formula (2), R₅ is selected from a hydrogenatom, an alkyl group, a substituted alkyl group, an alkoxy group, ahalogen atom, a CN, a ureido group and an NHCOR₆. The R₆ is selectedfrom a hydrogen atom, an alkyl group, a substituted alkyl group, an arylgroup, a substituted aryl group, an aralkyl group and a substitutedaralkyl group. In the formula (3), T represents an alkyl group, and W isselected from a hydrogen atom, a CN, a CONR₁₀R₁₁, a pyridium group, anda carboxyl group. R₁₀ and R₁₁ are each independently selected from ahydrogen atom, an alkyl and a substituted alkyl group. m represents analkylene chain having 2 to 8 carbon atoms. In the formula (4), B isselected from a hydrogen atom, an alkyl group and a carboxyl group.

R₁, R₂, R₃ and R₄ in the formula (C) each independently is selected froma hydrogen atom, an alkyl, and a substituted alkyl group. L represents adivalent organic linking group, and n represents 0 or 1. X eachindependently represents a carbonyl group or it is represented by thefollowing formulae (2), (3) or (4).

(Z in the above-mentioned formulae (2) to (4) each independently isselected from an OR₇, an SR₇ and an NR₈R₉, Y is selected from a hydrogenatom, a Cl, a CN and a Z, and E is selected from a Cl and a CN. R7₇, R₈and R₉ each independently represent a hydrogen atom, an alkenyl group, asubstituted alkenyl group, an alkyl group, a substituted alkyl group, anaryl group, a substituted aryl group, an aralkyl group, or a substitutedaralkyl group. Furthermore, R₈ and R₉ may form a 5- or 6-membered ringtogether with a nitrogen atom bonded therewith.)

When the compound of the general formula (C) does not have a sulfonicgroup, it has at least two groups selected from a carboxyl group and athiocarboxylic group, and the compound of the general formula (C) has asulfonic group(s) or the same number of a group(s) selected from acarboxyl group and a thiocarboxylic group as that of the sulfonicgroup.]

As the compounds represented by the above-mentioned general formula (C),for example, those mentioned below can be presented.

When the above-mentioned coloring materials are used in combination, theamount of the coloring material in the ink depends on the purpose andthe form of the use, and thus it is not particularly limited. However,in general, it is preferable in a range of 0.1 to 15% by mass withrespect to the ink total weight. More preferably, it is 0.1 to 10% bymass. At least as a part of the coloring material, the water-solublefluorescent coloring material having a plurality of the fluorescentgroups and a free sulfonic acid group as the water-soluble group of thepresent invention is used.

Moreover, when the above-mentioned coloring material used incombination, the ratio of the above-mentioned coloring material nothaving the fluorescence in the total coloring material to be used can beselected according to the characteristics of the desired fluorescenceemission, and it can be at least 0.1 to 20% by mass with respect to thetotal coloring material amount, and it is preferably at least 0.5 to 10%by mass.

Moreover, in the present invention, when a fluorescent coloring materialhaving a structure different from that of the present invention is usedin combination to increase the content of the coloring material in theink of the present invention, not only the decrease in the fluorescentintensity is suppressed, but also the fluorescent intensity is improved.As the fluorescent coloring material used here, either a dye and apigment can be used, but a dye is preferable because it provides the inkwith a large blurring rate on a recording medium and for obtaininghigher fluorescent intensity.

According to the present invention, whether the fluorescent coloringmaterial of the present invention is used alone as the coloringmaterial, a plurality of the fluorescent coloring materials of thepresent invention are used in combination, or the coloring material ofthe present invention and a fluorescent coloring material outside therange of the present invention are used in combination, the totalcontent of the coloring material is preferably 0.01 to 20% by mass withrespect to the ink total mass, and furthermore, 0.05 to 10% by mass.

As the other components used in the ink, it is preferable to use amixture of water and a water-soluble organic compound as the solventcomponent. As the water-soluble organic compound, for example, sugaralcohols such as glycerol and xylitol, amides such as dimethylformamide, and dimethyl acetamide; ketones such as acetone; ethers suchas tetrahydrofuran and dioxane; polyalkylene glycols such aspolyethylene glycol and polypropylene glycol; alkylene glycols having analkylene group of 2 to 6 carbon atoms such as ethylene glycol, propyleneglycol, butylenes glycol, triethylene glycol, 1,2,6-hexane triol,thiodiglycol, hexylene glycol, and diethylene glycol, lower alkyl ethersof a polyhydric alcohol such as ethylene glycol mono methyl (or ethyl)ether, diethylene glycol mono methyl (or ethyl) ether, and triethyleneglycol mono methyl (or ethyl) ether; N-methyl-2-pyrolidone,1,3-dimethyl-2-imidazolydinone, triethanol amine, sulforan, dimethylsulfoxide, 2-pyrolidone, or the like, those having the crystallineproperty, such as urea, ethylene urea, ε caprolacton, succinimide,thiourea, dimethylol urea, or the like can be presented, and oneselected therefrom, or as needed, two or more kinds selected can beused.

Moreover, to these compounds, at least one selected from ethylene oxide,propylene oxide and an alkyl can be added as a substituent, to improvethe fluorescence of the ink of the present invention applied on therecording material.

Moreover, it is preferable to use a crystalline compound having a cyclicstructure since the crystallization of the crystal forming compound inthe ink maintains sticking resistance of the ink and the stability ofthe image. The crystal forming component can be used alone or as neededas a combination of two or more kinds. Moreover, those being solid in anordinary temperature environment is preferable for the effect of thepresent invention owing to precipitation of the crystal component. Theabove-mentioned ordinary temperature environment means a range of 20° C.to 25° C. In consideration of the handling convenience, those having amelting point in the ordinary temperature environment of 30° C. or moreand preferably those having the melting point of 60° C. or more arepreferable, and further preferably, those having the melting point of120° C. or higher are preferable as the crystal forming component. Thecontent of the crystal forming component in the ink can be selectedaccording to the kind of the recording material, and it is preferably 1to 30% by mass with respect to the ink total mass, and furthermore, 2 to20% by mass. When it is too little, the effect of the present inventioncannot be realized, and when it is too much, an adverse effect is posedto the ejecting property in the case of use for the ink jet recording.

Moreover, the content of the above-mentioned water-soluble organiccompound is in general 1% to 40% by mass with respect to the ink totalmass, and more preferably it is in a range of 2% to 30% by mass.

Moreover, the water content of the ink is selected preferably in a rangeof 30 to 95% by mass. When it is less than 30% by mass, the solubilityof the water-soluble component may not be ensured, and furthermore, theink viscosity becomes higher. In contrast, when the water content ismore than 95% by mass, too much evaporating component preventssufficient adhesion characteristics.

As the constituent component of the ink of the present invention, it ispreferable to use a surfactant. As the surfactant, those of variouskinds can be used, and the preferable surfactants are a surfactanthaving a nonionic property or an anionic property.

When it has a cationic property, not only the color developing propertyand the reliability are deteriorated, but also it reacts with thecoloring material to be used so as to prevent appearance of the effectsof the present invention. However, an amphoteric surfactant may be useddepending on the state of the use. Furthermore, it is particularlypreferable to use a nonionic surfactant since the nonionic surfactantdoes not have a polarity with respect to the coloring material so as tohardly hinder the reliability. If the surfactant has a polarity, it willdeter the fluorescence emitting property of the ink.

Moreover, it is preferable that the surfactant will not cause phaseseparation from an aqueous solution or from an ink not containing acoloring material. If the surfactant causes phase separation, the inkbecomes instable, and it tends to adsorb to the ink storage memberlowering the effect of the present invention and reliability of therecording apparatus of the present invention, and thus it is notpreferable.

This means that use of a surfactant that apparently dissolves ordisperses homogeneously in water is preferable. Moreover, even asurfactant that causes phase separation from an aqueous solution or inkexcluding the coloring material can be used in a state apparentlydissolved or dispersed homogeneously in water, e.g., in an emulsionstate, by concomitant use of another surfactant.

Moreover, by using the surfactant in the ink at a critical micelleconcentration or more, more preferable result can be obtained. This isbecause with the content is equal to or higher than the critical micelleconcentration, diffusion of the ink droplet on the recording materialbecomes preferable with most of the recording materials, so that thefluorescent coloring material tends to adsorb onto the constituentcomponent of the recording material in a monomolecular state, that is,aggregation or association of the fluorescent coloring material can beprevented.

Moreover, surfactants having a small difference between the dynamicsurface tension and the static surface tension are preferable. If thedifference is small, the orientation speed of the surfactant is highaccelerating wetting of the interface of the recording material with theink droplet. Thus the effect of the present invention is improved.

Moreover, a surfactant having a poor solubility in water or ink can beused in combination with another surfactant forming composite micellesor an emulsion state in the ink or the aqueous solution for use.

Among the nonionic surfactants, those having the HLB of 15 or less canbe used preferably in the present invention. This is because, althoughthe effect of the present invention can be obtained with a surfactanthaving a good water solubility, the water solubility is so high if theHLB is more than 15 that the wettability or diffusing property of theink droplet with the recording material becomes undesirable, and thusthe mechanism effect of the present invention can not be realizedsufficiently.

The content of the nonionic surfactant in the ink of the presentinvention is specifically 1% by mass or more with respect to the inktotal mass, and it is further preferably 1 to 20% by mass. When it isless than 1% by mass, the desired ink permeating property and spreadingproperty may not be obtained in the image formation. Moreover, when itis more than 20% by mass, the balance of the desired printing qualities,for example, the preferable balance of various performances such as theimage density, the image fixing property, prevention of feathering(beard-like blurring) may not be kept.

Among the nonionic surfactants satisfying the above-mentionedconditions, those particularly preferable for the constituent componentof the ink of the present invention include the following compoundsrepresented by the general formula (I) and the compounds represented bythe following (II) to (VII) can be presented, but not limited thereto.

[In the above-mentioned general formula (I), A and B each independentlyrepresent C_(n)H_(2n-1) (N is an integer from 1 to 10), and X and Y eachrepresents an open ringed ethylene oxide unit and/or an opened propyleneoxide unit.]

Moreover, among the nonionic surfactants represented by theabove-mentioned general formula (I), particularly preferable are thecompounds represented by the following general formula (VIII).

(m and n are an integer, respectively.)

In view of the ink stability, it is preferable that the ink of thepresent invention further contains a monohydric alcohol. The monohydricalcohol prevents microbial growth such as fungi that may cause clogging.Furthermore, monohydric alcohol can enhance the effects of the presentinvention because it accelerates evaporation or permeation of the inkapplied onto a recording material. The content of the monohydric alcoholin the ink of the present invention is 0.1 to 20% by mass with respectto the total ink mass, preferably 0.5 to 10% by mass. Specific examplesof the monohydric alcohol usable for the ink of the present inventioninclude ethanol, isopropyl alcohol, n-butanol, or the like, and they canbe used alone or in combination of two or more kinds as required.

As needed, the ink of the present invention may further include variouskinds of additives such as a water-soluble organic solvent, asurfactant, a corrosion preventing agent, an antiseptic agent, a funguspreventing agent, an antioxidant, an antireductant, an evaporationpromoting agent, a chelating agent, a water-soluble polymer, and a pHadjusting agent.

According to the present invention, the surface tension of the ink is 40mN/m or less, and furthermore, 30 to 40 mN/m, because it is preferablefor a liquid droplet to occupy a certain area after recording, in viewof the mechanism expression explained above. Moreover, the pH of the inkof the present invention is preferably 6.5 or more in terms of the inkstability.

Furthermore, according to the ink of the present invention, it ispreferable to use a plurality of alkali metal ion species as the counterion for the coloring material. When the ink is used for ink jetrecording, combination use of the coloring material and the alkali metalion can improve the stability and ejection properties of the ink. As thealkaline metal ions, Li⁺, Na⁺, K⁺, or the like can be listed.

As the method and the apparatus preferable for recording with the ink ofthe present invention, a method and an apparatus for providing thermalenergy in accordance with the recording signal to the ink in the chamberof the recording head, and generating liquid droplets by the thermalenergy can be presented.

Although the water-based ink of the present invention provided asmentioned above is used as an ink for the ordinary stationery, it isparticularly effective at the time of use in the ink jet recording. Asthe ink jet recording method, there are a recording method of ejectingliquid droplets by applying a mechanical energy to the ink, and an inkjet recording method of ejecting liquid droplets by bubbling of the inkby applying a thermal energy to the ink. In particular, it is preferablefor the case of use in the ink jet recording method of the type ofejecting the ink by the ink bubbling phenomenon by the thermal energy sothat the characteristics of the extremely stable ejection withoutgeneration of the satellite dots, or the like can be provided. However,in this case, the thermal physical property values (such as the specificheat, the coefficient of the thermal expansion, and the coefficient ofthe thermal conductivity) may be adjusted.

Furthermore, in view of solving the problem of water resistance of theink printed or recorded on plain paper, and of good matching with theink jet head, it is preferable that the viscosity of the ink of thepresent invention at 25° C. is adjusted to 15 cP or less, preferably 10cP or less, and more preferably 5 cP or less. Therefore, in order toadjust the ink to the above-mentioned physical properties for solvingthe problems with the plain paper, the water content included in the inkof the present invention is 50% by mass or more and 98% by mass or less,and more preferably 60% by mass or more and 95% by mass or less.

It is preferable that the present invention is used for the fluorescenceemission for the purpose of the measurement or judgment in the visiblelight region by the excitation wavelength in the predeterminedultraviolet region. When a conventional aqueous fluorescent dye is usedfor an ink, the water resistance is poor and the fluorescence intensityis weak. Thus when another coloring material is mixed in the ink,desired performance cannot be obtained. On the contrary, the ink of thepresent invention can provide good water resistance and fluorescentintensity. Accordingly, among a number of the ink identificationapplications, it can be used for authenticity determination of theprinted matter, for example, of securities and the like.

The present invention provides excellent effects in the ink jetrecording head and recording apparatus that carry out recording byejecting liquid droplets utilizing thermal energy.

As the representative configuration and principal thereof, for example,those using the basic principals disclosed in the specification of theU.S. Pat. No. 4,723,129, and the specification of the U.S. Pat. No.4,740,796 are preferable. The method can be utilized either to theso-called on demand type or the continuous type. Particularly in thecase of the on demand type, it is effective since the thermal energy isgenerated in the electro-thermal converter by applying at least onedriving signal for providing the rapid temperature rise exceeding thenuclear boiling point according to the recording information to thesheet with the liquid (ink) sustained or the electro-thermal converterdisposed corresponding to the liquid channel for generating the filmboiling in the heater surface of the recording head so as toconsequently form a bubble in the liquid (ink) according to the drivingsignal one by one. By ejecting the liquid (ink) via the ejection openingaccording to the growth and the contraction of a bubble, at least onedroplet is formed. By providing the driving signal in a pulse shape,since the bubble growth and contraction can be executed instantaneouslyand appropriately, ejection of the liquid (ink) can be achieved with theexcellent response property, and thus it is more preferable.

As the driving signal with the pulse shape, those disclosed in thespecification of the U.S. Pat. No. 4,463,359 and the specification ofthe U.S. Pat. No. 4,345,262 are suitable. With the conditions disclosedin the specification of the U.S. Pat. No. 4,313,124 of the inventionrelated to the temperature rise ratio of the above-mentioned heatfunctioning surface, the excellent recording can be executed.

As to the recording head configuration, in addition to the combinationconfiguration of the ejection opening, the liquid channel and theelectro-thermal converter as in the above-mentioned specifications (thestraight line liquid channel or the right angle liquid channel), theconfiguration using the specification of the U.S. Pat. No. 4,558,333 andthe specification of the U.S. Pat. No. 4,459,600 disclosing theconfiguration with the heat functioning part disposed in a bent regionis also included in the present invention.

Additionally, the present invention is effective also in theconfiguration based on Japanese Patent Application Laid Open No.59-123670 disclosing the configuration of having a common slit as theejecting part of the electro-thermal converters with respect to aplurality of the electro-thermal converters, and the configurationJapanese Patent Application Laid Open No. 59138461 corresponding to theejecting part with the open hole for absorbing the pressure wave of thethermal energy.

Furthermore, as the recording head of the full line type having a lengthcorresponding to the width of the maximum recording medium to berecorded by the recording apparatus, either the configuration ofsatisfying the length according to the combination of a plurality ofrecording heads as disclosed in the above-mentioned specification, orthe configuration of a recording head formed integrally can be employed,and the present invention can achieve the above-mentioned effectsfurther effectively.

Additionally, the present invention is effective also in the case ofusing a replaceable chip type recording head capable of achievingelectric connection with the apparatus main body or the ink supply fromthe apparatus main body by being mounted on the apparatus main body, ora cartridge type recording head with the ink tank provided integrally inthe recording head itself.

Moreover, it is preferable to provide recovery means, preliminaryauxiliary means, or the like for the recording head as the configurationof the recording apparatus of the present invention for furtherstabilizing the effect of the present invention. As the specificexamples thereof, capping means for the recording head, cleaning means,pressuring or vacuuming means, electro-thermal converter, anotherheating element, or preliminary heating means as a combination thereofcan be presented, and execution of a preliminary ejection mode forexecuting the ejection other than recording is also effective for stablerecording.

Furthermore, not only for the apparatus of the main color recording modesuch as black, the present invention is extremely effective for anapparatus of multicolor mode or full color mode by color mixing, usingan integrated head or a combination of plural heads.

Although in the embodiments of the present invention described above,the ink is explained as a liquid, the ink can be one that solidifies ata temperature lower than room temperature but softens or liquefies atroom temperature, or one being liquid only when the recording signal isapplied since it is common for the above explained ink jet system tocontrol the ink temperature in a range of 30° C. or more and 70° C. orless so as to control the ink viscosity at the stable ejection range.

Additionally, the ink that liquefies only by application of the thermalenergy can be used in the present invention, for example, an inkactively utilizing the thermal energy for the energy for the phasechange of the ink from the solid state to the liquid state to preventtemperature rise, or an ink that solidifies when left standing toprevent the ink evaporation, one liquefies by application of the thermalenergy according to the recording signal so as to be ejected as aliquid, but solidifies before landing on the recording medium. In thiscase, the ink may be provided in a form facing the electro-thermalconverter in a state held in a porous sheet recessed part or a throughhole as a liquid or a solid matter as disclosed in Japanese PatentApplication Laid-Open No. S54-56847, or Japanese Patent ApplicationLaid-Open No. S60-71260. In this embodiment, the most effective for theabove-mentioned inks in one for executing the above-mentioned filmboiling method.

Furthermore, the form of the recording apparatus according to thepresent invention includes a copying unit in combination with a reader,or a facsimile unit having the function of transmission and receipt, aswell as an image outputting terminal of an information processingappliance such as a word processor and a computer, provided integrallyor independently.

Moreover, the ink of the present invention may be used as a coloringmaterial for a colored pixel of a color filter such as a liquid crystaldisplay panel. The coloring material may be used alone or in combinationwith another coloring material for the color adjustment. As the methodfor forming a colored pixel, a production method of applying an ink on asubstrate by the ink jet recording method is preferable, however, it isnot limited thereto.

EXAMPLES

Next, with reference to the examples and the comparative examples, thepresent invention will be explained more specifically. In thedescription, the part and % are based on the mass unless otherwisespecified.

Example 1

Ink Composition: Coloring material of the compound (A) (water-soluble0.05% fluorescent coloring material Glycerol   10% Triethylene glycol  10% N + m = 10 in the compound of the formula (III)  0.5% Pure waterthe rest

Example 2

Ink Composition:

The content of the coloring material compound (A) in Example 1 waschanged to 0.5%.

Example 3

Ink Composition:

The content of the coloring material compound (A) in Example 1 waschanged to 1.0%.

Example 4

Ink Composition:

The content of the coloring material compound (A) in Example 1 waschanged to 2.0%.

Comparative Example 1

Ink Composition: C.I. Acid Yellow 73 (water-soluble fluorescent 0.05%coloring material) Glycerol   10% Triethylene glycol   10% N + m = 10 inthe compound of the formula (III)  0.5% Pure water the rest

Comparative Example 2

Ink composition

The water-soluble fluorescent coloring material content in ComparativeExample 1 was changed to 0.5%.

Comparative Example 3

Ink Composition

The water-soluble fluorescent coloring material content in ComparativeExample 1 was changed to 1.0%.

Comparative Example 4

Ink Composition

The water-soluble fluorescent coloring material content in ComparativeExample 1 was changed to 2.0%.

Comparative Example 5

Ink Composition:

The water-soluble fluorescent coloring material in Comparative Example 1was changed to C. I. Solvent Green 7, and the content is changed to2.0%.

<Evaluation>

(Fluorescent Property Evaluation)

The inks of Examples 1 to 3 and Comparative Examples 1 to 3 were leftunder the 60° C. environment to evaporating water in the ink until asubstantially constant weight was reached. Then the fluorescentintensity was measured by irradiating light of 254 nm excitationwavelength using a commercially available fluorescent measuringapparatus FP-750 (produced by JASCO). The obtained results are shown inFIGS. 1 and 2.

As the comparison between FIG. 1 and FIG. 2 shows, the inks of Exampleshave the stable fluorescent intensity even when the content of thefluorescent coloring material in the ink is increased compared with theinks of Comparative Examples.

(Water Resistance Evaluation)

The inks of Examples and Comparative Examples were loaded in acommercially available ink jet recording apparatus BJS600 (Canon) forprinting alphanumerals, and a solid image of 50% duty on a commerciallyavailable bond paper. After leaving for one day after the printingoperation, it was soaked in tap water for 5 minutes.

The inks of Examples 1 to 3: Even after soaking in tap water, thereadability of the alphanumerals was not changed significantly comparedwith the state before soaking. Moreover, the density residual rate ofthe 50% duty solid print was 80% or more in all cases.

The inks of Comparative Examples 1 to 3: By soaking in tap water, thealphanumerals became hardly readable. Moreover, the density residualrate of the 50% duty solid print was 50% or less in all cases.

Fluorescent Property Evaluation on the Recording Material (1)

The inks of Example 4 and Comparative Examples 4 and 5 were loaded in acommercially available ink jet recording apparatus BJS600 for printing asolid image of 50% duty on a commercially available Kraft paper. Afterleaving for one day in the 60° C. environment after printing, thefluorescent intensity was measured by irradiating light of 254 nmexcitation wavelength using a commercially available fluorescentmeasuring device FP-750 (produced by JASCO). The obtained results areshown in FIG. 3.

The ink of Example 4 showed an remarkably high fluorescent intensitycompared with the inks of Comparative Examples.

Conventionally, the content of a fluorescent coloring material in theink cannot be increased owing to decrease in fluorescent intensity(concentration quenching). According to the present invention, thecontent of the fluorescent coloring material can be increased toincrease fluorescent intensity or another fluorescent coloring materialor a non-fluorescent coloring material can coexist in the ink withoutcausing decrease in fluorescent intensity, and furthermore, the highfluorescent intensity of the recorded image on the recording materialcan be obtained. Moreover, the water resistance of the recorded imagecan be improved. Furthermore, when the ink of the present invention isused for an ink jet recording printer, no problem occurs in view ofclogging of the nozzle for ejecting the ink droplets and the ejectingproperty so that a printing and recording operation can be executedpreferably. Moreover, the ink of the present invention has also a goodsticking resistance.

This application claims priority from Japanese Patent Application No.2003-127617 filed on May 2, 2003, which is hereby incorporated byreference herein.

1. A water-based fluorescent ink to be used for measurement or judgmentof a fluorescence in a visible light region that is emitted byirradiation of an excitation light of a predetermined excitationwavelength in an ultraviolet region, the ink comprising water, acoloring material that dissolves or disperses in water, and an organicsolvent, wherein the coloring material has a plurality of fluorescentgroups and a sulfonic acid group as a water-soluble group in a structurethereof in the state of a free acid.
 2. The water-based fluorescent inkaccording to claim 1, wherein the coloring material is a hardlywater-soluble coloring material.
 3. The water-based fluorescent inkaccording to claim 2, wherein the hardly water-soluble coloring materialhas a solubility in water less than 3% by mass.
 4. The water-basedfluorescent ink according to claim 1, wherein the coloring material hasa substantivity property with a cellulose fiber.
 5. The water-basedfluorescent ink according to claim 1, wherein the plurality of thefluorescent groups of the coloring material are of one kind.
 6. Thewater-based fluorescent ink according to claim 1, wherein the pluralityof the fluorescent groups are linked via a linking group.
 7. Awater-based fluorescent ink to be used for measurement or judgment of afluorescence in a visible light region emitted by irradiation of anexcitation light of a predetermined excitation wavelength in anultraviolet region, the ink comprising water, a coloring material thatdissolves or disperses in water, and an organic solvent, wherein thecoloring material has a plurality of fluorescent groups and a sulfonicacid group as a water-soluble group in a structure thereof in the stateof a free acid, and wherein the ink is visible under an ordinary lightin a visible light region.
 8. The water-based fluorescent ink accordingto claim 7, wherein the coloring material has a solubility in water lessthan 3% by mass.
 9. The water-based fluorescent ink according to claim7, wherein the coloring material has a substantivity property with acellulose fiber.
 10. The water-based fluorescent ink according to claim7, wherein the plurality of the fluorescent groups of the coloringmaterial are of one kind.
 11. The water-based fluorescent ink accordingto claim 1, wherein the plurality of the fluorescent groups are linkedvia a linking group.
 12. A recorded image formed with a water-basedfluorescent ink to be used for measurement or judgment of a fluorescencein a visible light region that is emitted by irradiation of anexcitation light of a predetermined excitation wavelength in anultraviolet region, wherein the ink comprises water, a coloring materialthat dissolves or disperses in water, and an organic solvent, andwherein the coloring material has a plurality of fluorescent groups anda sulfonic acid group as a water-soluble group in a structure thereof inthe state of a free acid.
 13. An method for judging authenticity of anink comprising irradiating an ultraviolet ray to an image formed with awater-based fluorescent ink, wherein the water-based fluorescent inkemits a fluorescence in a visible light region by irradiation of anexcitation light of a predetermined excitation wavelength in anultraviolet region, and wherein the ink comprises water, a coloringmaterial that dissolves or disperses in water, and an organic solvent,wherein the coloring material has a plurality of fluorescent groups anda sulfonic acid group as a water-soluble group in a structure thereof inthe state of a free acid.
 14. The ink judging method according to claim13, wherein the coloring material has a solubility in water less than 3%by mass.
 15. The ink judging method according to claim 13, wherein thecoloring material has a substantivity property with a cellulose fiber.16. The ink judging method according to claim 13, wherein the pluralityof the fluorescent groups of the coloring material are of one kind. 17.The ink judging method according to claim 13, wherein the plurality ofthe fluorescent groups are linked via a linking group.
 18. A method forjudging authenticity of an image comprising irradiating an ultravioletray to an image formed with a water-based fluorescent ink, wherein thewater-based fluorescent ink emits a fluorescence in a visible lightregion by irradiation of an excitation light of a predeterminedexcitation wavelength in an ultraviolet region, and wherein the inkcomprises water, a coloring material that dissolves or disperses inwater, and an organic solvent, wherein the coloring material has aplurality of fluorescent groups and a sulfonic acid group as awater-soluble group in a structure thereof in the state of a free acid.19. The ink judging method according to claim 18, wherein the coloringmaterial has a solubility in water less than 3% by mass.
 20. The inkjudging method according to claim 18, wherein the coloring material hasa substantivity property with a cellulose fiber.
 21. The ink judgingmethod according to claim 18, wherein the plurality of the fluorescentgroups of the coloring material are of one kind.
 22. The ink judgingmethod according to claim 18, wherein the plurality of the fluorescentgroups are linked via a linking group.